[Bug 75502] [SNB, IVB] Page flips hang indefinitely, apparently waiting for mmio writes that never happen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=75502

--- Comment #21 from Chris Wilson <chris at chris-wilson.co.uk> ---
To double check the theory that the scanout went awol, can you please try with

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
b/drivers/gpu/drm/i915/i915_debugfs.c
index 94aabfc63c3d..c6b81e59058d 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -611,16 +611,28 @@ static int i915_gem_pageflip_info(struct seq_file *m,
void *data)
                                seq_puts(m, "Stall check waiting for page flip
ioctl, ");
                        seq_printf(m, "%d prepares\n",
atomic_read(&work->pending));

+                       {
+                               u32 addr;
+
+                               if (INTEL_INFO(dev)->gen >= 4)
+                                       addr = DSPSURF(crtc->plane);
+                               else
+                                       addr = DSPADDR(crtc->plane);
+
+                               seq_printf(m, "Current scanout address
0x%08lx\n", 
+                                          I915_READ(addr));
+                       }
+
                        if (work->old_fb_obj) {
                                struct drm_i915_gem_object *obj =
work->old_fb_obj;
-                               seq_printf(m, "Old framebuffer gtt_offset
0x%08lx\n",
+                               seq_printf(m, "Old framebuffer address
0x%08lx\n",
                                           i915_gem_obj_ggtt_offset(obj));
                        }
                        if (work->pending_flip_obj) {
                                struct drm_i915_gem_object *obj =
work->pending_flip_obj;
                                bool complete;

-                               seq_printf(m, "New framebuffer gtt_offset
0x%08lx\n",
+                               seq_printf(m, "New framebuffer address
0x%08lx\n",
                                           i915_gem_obj_ggtt_offset(obj));

                                if (INTEL_INFO(dev)->gen >= 4) {

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